Information on the fetal and perintal biology of the human fetus, particularly during the last half of gestation, and of the newborn is not readily available. Therefore, studies on the rhesus monkey (M. mulatta), which is biologically similar to the human primate, are invaluable. The overall purpose of our studies is to acquire information on the metabolic control mechanisms and the interrelations of carbohydrate, lipid, and amino acid metabolism in the rapidly growing (fetal and neonatal) and adult muscles of rhesus monkeys. We are investigating the levels of cyclic AMP and the effect of the various prostaglandins--PGE, PGE2, PGF1 alpha, and PGE2 alpha--on this compound in fetal heart, diaphragm, and voluntary skeletal muscle. We are also planning to investigate the difference between the kinetics of fetal and adult 3' 5' AMP phosphodiesterase(s) and the sensitivity of this enzyme(s) to the methylxanthines. In our study of rate-limiting reactions, we are 2 approaches. 1) Rates of product formation from various substrates--for example, lactate-C14 formation from C14-precusors in the glycolytic pathways, such as fructose-6-PO4 and fructose-1-6-diPO4--will be compared. The C14 effect of cAMP, ATP. citrate, and other effector molecules on the production of lactate-C14 from C14-precursors such as fructose-6-PO4 will be measured. 2) The mass-action ratios in situ will be determined and compared with apparent equilibrium constants. The effects of altered glycolytic flux rates on the intracellular contents of relevant metabolics intermediates and cofactors will also be investigated. Although carbohydrate was long believed to be the major fuel for adult muscle, it is now generally accepted that lipid, and even amino acids, serve as significant energy sources. Because the fetus receives a continuous supply of glucose from its mother through the placenta, it has been assumed that the major or sole metabolic fuel of the fetus is carbohydrate. Currently we are studying the oxidation of albumin-bound free fatty acids and amino acids by fetal muscles.